Embodiments of the present invention relate generally to disc replacement therapy. More particularly, embodiments of the present invention relate to devices, materials and methods that can be used in disc replacement therapy procedures.
Generally, a healthy mammalian spine includes a series of vertebrae with discs located in an intervertebral space between each of the adjacent vertebrae. The discs of the spine function to allow motion and to distribute vertical axial loads on the spine. Discs generally are formed of an annulus fibrosis, which creates a disc perimeter, and a gel-like nucleus material, which is positioned within the annulus fibrosis. The healthy nucleus acts essentially as an incompressible fluid within a container, the annulus. The nucleus is compressed by the vertical forces on the spine and deforms horizontally to distribute the vertical load into the disc annulus.
Certain spinal disorders can cause damage to the disc. For example, one type of spinal disorder is a “herniated disc,” which occurs when a portion of the disc nucleus presses out a hole or herniated region in the surrounding annulus. When this happens, the extruded nucleus material can press on nerves in the spinal region, causing back or spinal pain.
Pain can vary in herniated disc patients from very little to debilitating, and movement can, at times, intensify the pain. Numbness and muscle weakness also may occur. If the pressure on the nerve root is great, the legs can be paralyzed. Further, if the cauda equina (the bundle of nerves extending from the bottom of the cord) is affected, control of bladder and bowels also can be lost. If these serious symptoms develop, medical attention is required immediately.
Some patients with herniated discs recover without corrective measures. Many others, however, require surgery. In severe cases, surgery may require removal of all of a disc and perhaps part of a vertebra. For example, treatments for herniated or ruptured discs can include spinal fusion and/or disc nucleus replacement. Spinal fusion includes removal of the disc nucleus and in some cases the annulus. The adjacent vertebrae then is fixed in position to the open space often times by some structure placed between the two vertebrae. A bone growth supplement then can be placed within this space to stimulate the adjacent bone and/or vertebrae to grow into this space causing them to merge or fuse together. The disadvantage to this procedure, however, is the loss of the shock absorbing feature and mobility of a healthy disc.
Another possible treatment for herniated or ruptured discs is disc nucleus replacement. In this treatment, the disc nucleus is fully or partially removed and replacement material or structures are placed within the annulus. The replacement material or structures provide at least some load bearing function of the former nucleus and allows spinal motion at the effected disc level.
While some nucleus replacement materials and methods currently are known, further improvements are needed. Thus, needs exist for nuclear disc replacement materials and structures that can be introduced through minimally invasive procedures and also remain within the nuclear space without a future risk of extrusion.